Hydraulic shock absorber

Abstract

In a shock absorber of a vehicle, when a moving speed of a piston rod in relation to a cylinder tube is slow and first and second input forces are externally applied to the shock absorber, damping forces of pressure side and extension side first damping force generating devices are larger than that of pressure side and extension side second damping force generating devices. On the other hand, when the moving speed is fast, the damping forces of the pressure side and the extension side second damping force generating devices are larger than that of the pressure side and the extension side first damping force generating devices. A gas enclosure chamber filled with gas is connected to a first chamber through a free piston.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a hydraulic shock absorber in which the damping force characteristics using a bulk modulus of a hydraulic fluid can be obtained more effectively when the moving speed of a piston rod in relation to a cylinder tube is slow as in the initial stage of compression action and extension action, and in a case in which the hydraulic shock absorber repeats the compression action and the extension action by external first and second input forces.[0003]2. Description of the Related Art[0004]A conventional type of hydraulic shock absorber is shown in JP-A-Hei 10-331898. According to this document, the hydraulic shock absorber is slidably inserted in a cylinder tube in the axial direction, and the hydraulic shock absorber includes first and second pistons for dividing the inside of the cylinder tube into a first chamber, an intermediate chamber, and a second chamber from one end to another end in thi...

AI Technical Summary

Benefits of technology

[0045]As a result, if the shock absorber is equipped on a vehicle, the vehicle provides a soft impression to a driver at the initial stage of the extension action of the shock absorber when the second input force is applied. Therefore, the driving feel of the vehicle is improved, and the advantageous effects are more reliably achieved.

[0046]When the moving speed during the extension action increases, the damping force of the extension side second damping force generating device becomes larger than that of the extension side first damping force generating device, then the extension side second damping force generating device predominantly generates the damping force. Therefore, the second chamber in front of the moving direction of the second piston compresses, and its hydraulic pressure increases.

[0047]Here, the capacity of the second chamber alone is small, so the volume change amount by the “bulk modulus” of the oil in the second chamber is small (hard). Therefore, according to the extension action of the second piston, the increase in speed of the hydraulic pressure in the second chamber becomes faster, then the response in the extension side second damping force generating device becomes higher.

[0048]As a result, if the shock absorber is equipped on a vehicle, the impact energy based on the second input force is immediately absorbed by the extension side second damping force generating device, when the moving speed is fast during the extension action of the shock absorber by the second input force. Therefore, another advantageous effect is an improved driving stability of the vehicle is more reliably produced.

[0049]According to another preferred embodiment of the present invention, the pressure side and the extension side first damping force generating devices may include pressure side and extension side first valves for allowing oil to pass through the first piston by the first hydraulic pressure difference between the first chamber and the intermediate chamber when the first and the second input forces are applied, and may include a first orifice that extends through the first piston. And the pressure side and the extension side second damping force generating devices may include pressure side and extension side second valves for allowing oil to pass through the second piston by the second hydraulic pressure difference between the intermediate chamber and the second chamber when the first and the second input forces are applied, and may include a second orifice that extends through the second piston. The open valve pressure characteristics of the pressure side and the extension side first valves may be lower than that of the pressure side and the extension side second valves. The cross-section of the first orifice may be smaller than that of the second orifice.

[0050]By providing the above configuration, at the initial stage of the compression action of the shock absorber, the second chamber is expanded by the entering action of the first and the second pistons into the cylinder tube, and its hydraulic pressure decreases. In order to make up the shortage of oil in the second chamber, generally the same amount of oil flows from the first chamber and intermediate chamber through the first orifice in the first piston and the second orifice in the second piston toward the second chamber. Therefore, the hydraulic pressure in the intermediate chamber decreases in relation to the hydraulic pressure in the first chamber. Also, the hydraulic pressure in the second chamber decreases in relation to the hydraulic pressure in the intermediate chamber.

Problems solved by technology

Thus, at the initial stage of the compression action of the shock absorber, the driver tends to be given a hard impression, because the response is high.

This is not preferable since it fails to improve driving comfort of the vehicle.

Therefore, a driver tends to be given a hard impression from the vehicle even at the initial stage of the extension action of the shock absorber, and the same problem as mentioned above may occur.

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